Electrical energy is applied to the brain to treat a variety of clinical conditions such as movement disorders or chronic pain. One method of delivering electrical energy to the brain involves inserting an electrical stimulation lead through a burr hole formed in the skull and then positioning the lead in a precise location adjacent a target area of the brain to be stimulated such that stimulation of the target area causes a desired clinical effect. For example, one desired clinical effect may be cessation of tremor from a movement disorder such as Parkinson's Disease. A variety of other clinical conditions may also be treated with deep brain stimulation, such as essential tremor, tremor from multiple sclerosis or brain injury, or dystonia or other movement disorders. The electrical stimulation lead implanted in the brain is connected to an electrical signal generator implanted at a separate site in the body, such as in the upper chest.
Electrical stimulation leads implanted in the brain require precise placement because of the relatively small size of the target area in the brain and because of the relatively close proximity of other non-targeted anatomic regions in the brain. One method of achieving precise placement is through a stereotactic surgical procedure that uses radiographic or fluoroscopic images of the brain to guide the surgeon to the target area. This may require placement of a three-dimensional frame to the head such that horizontal and vertical coordinates of the target area may be compared to radiographic images and precisely located. Other stereotactic methods may include a frameless procedure. Once the precise location of an electrical stimulation lead in the brain is achieved it is important that the lead remain in its precise position to avoid injury to the brain, reduced effectiveness, or other undesirable effects. An electrical stimulation lead may be particularly prone to being dislodged when a stereotactic frame is disassembled and removed from the head, for example, after insertion of the lead. When the frame is being disassembled and removed from around the insertion site, a doctor, nurse, or other clinician must typically attempt to manually secure the exposed end of the electrical stimulation lead in an attempt to maintain the precise positioning of the lead in the brain. This is difficult, if not impossible, to accomplish in practice.
Previous burr hole covers used for securing an electrical stimulation lead in position in a person's brain have included a fluid-impermeable membrane that spans the entire central aperture of the burr hole cover to prevent leakage of cerebrospinal fluid (CSF) from the brain. In these previous burr hole covers the fluid-impermeable membrane has been solid and the electrical stimulation lead is forced through the fluid-impermeable membrane to form a puncture hole in which the lead is then secured. Certain of these previous fluid-impermeable membranes have included an upper portion with one or more pre-formed blind holes above the solid lower portion that is punctured to form a hole for securing the electrical stimulation lead. With or without blind holes, when the electrical stimulation lead is secured in the puncture hole, the fit of the lead within the puncture hole and the fluid-impermeable nature of the surrounding membrane prevent CSF leakage from the brain. The puncture hole formed through the fluid-impermeable membrane, and any associated blind hole, is preferably sized such that upon removal of the electrical stimulation lead the fluid-impermeable membrane reseals and CSF leakage continues to be prevented.